On Mon, Aug 26, 2013 at 2:33 AM, Zhang <[email protected]> wrote: > Hi, Matt > BTW, > > Could you leave me any suggestion of those direct solver PC, such as > superLU_dist? Thanks
For simple Poisson, I do not expect direct methods to be competitive with MG, however you can easily try by configuring with --download-superlu and -pc_type lu -pc_factor_mat_solver_package superlu Matt > Zhenyu > > > -----原始邮件----- > *发件人:* "Matthew Knepley" <[email protected]> > *发送时间:* 2013-08-24 18:20:00 (星期六) > *收件人:* Zhang <[email protected]> > *抄送:* [email protected] > *主题:* Re: [petsc-users] which is the best PC for GMRES Poisson solver? > > On Sat, Aug 24, 2013 at 12:07 AM, Zhang <[email protected]> wrote: > >> Hi, >> >> Recently I wrote a code of projection method for solving the >> incompressile flow. It includes a poisson solution of pressure. >> I transfered the code to be based on Petsc . >> > > Use -pc_type gamg > > Matt > > >> However, in the case of 3D lid-driven flow case, the speed of petsc >> version is not advantageous yet. >> >> I tried different combination of preconditioner with GMRES solver. Among >> them GMRES+PCILU or GMRES+SOR are both the fastest. >> For a grid 80x80x80, GMRES+SOR serial version used 185.816307 secs. >> However, for case 120x120x120, it diverged. So is GMRES+PCILU. >> >> Then I tried a parallel comparison, as follows, >> >> >> >> ############################################################################################# >> # with Petsc-3.4.2, time comparison (sec) >> # size (80,80,80), 200 steps, dt=0.002 >> #debug version 177.695939 sec >> #opt version 106.694733 sec >> #mpirun -np 8 ./nsproj ../input/sample_80.zzy.dat -ksp_type gmres -p >> c_type hypre -ksp_rtol 1.e-2 >> #debug version 514.718544 sec >> #opt version 331.114555 sec >> #mpirun -np 12 ./nsproj ../input/sample_80.zzy.dat -ksp_type gmres >> -pc_type hypre -ksp_rtol 1.e-2 >> #debug version 796.765428 sec >> #opt version 686.151788 sec >> #mpirun -np 16 ./nsproj ../input/sample_80.zzy.dat -ksp_type gmres >> -pc_type hypre -ksp_rtol 1.e-2 >> >> I do know sometimes problem with speed is not due to petsc, but my own >> code, so please you are welcome for any suggestion >> about which combination is the best for such a computation. I know >> solving Poiison and Helmholtz is so common to see in numerical work. >> Thank you first. >> >> BTW, I also tried to use superLU_dist as PC. >> #mpirun -np 16 ./nsproj ../input/sample_20.zzy.dat -ksp_type gmres >> -pc_type lu -pc_factor_mat_solver_package superlu_dist -ksp_rtol 1.e-2 >> >> But with 16 nodes, except case of 20x20x20 grids, all larger grids run e >> xtremly slow. >> Since I never use the direct PC before, is it true that a good usage of >> direct LU as Preconditioner >> requires that the amount of procedures be much larger so that for each >> node the calculation of direct solver is smalled enough to use it? >> >> Cheers, >> >> Zhenyu >> > > > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
